This disclosure relates generally to radiation detection and, more specifically, to pyroelectric detection systems and methods of making the same.
Pyroelectric detection systems (also known as optical pyrometers) are commonly used to measure the temperature of a radiation emitting object by projecting the radiation by a lens to a sensing element sensitive to selected wavelengths. For example, the lens can transmit infrared radiation to a sensing element, which converts the infrared radiation to an electrical signal that can be displayed in units of temperature after compensating for ambient temperature variation. Thus, the temperature of an object can be measured without actually contacting the object. The sensing element can comprise a pyroelectric material, i.e., a crystalline structure that can produce current when excited with a change in infrared (IR) energy.
One application of a pyroelectric detection system is in a hot box detector of a train inspection system. In particular, the pyroelectric detection system can be used to detect when the radiation emitted by a train part, such as a wheel bearing or a wheel brake, exceeds a certain threshold at which the operation of the train could be dangerous. For example, the train part could overheat as a result of locked train break or mechanical failure of the train part (e.g., the bearing). A controller in electrical communication with the detection system could send a signal to stop the train when the radiation exceeds the threshold.
There is a growing demand in the train industry to make such pyroelectric detection systems more compact. One way to increase the compactness of a pyroelectric detection system is to shrink the distance from the lens to the sensing element by using a lens having a shorter focal length. However, since the train part dimension is fixed and the distance from the target to the lens is fixed, the shorter focal-length lens has a higher magnification ratio, i.e., the ratio of the size of the target to the size of its image on the sensing element. Thus, radiation outside the desired target area of the train can undesirably reach the sensing element, confusing the decision as to whether a radiation threshold has been exceeded.
A need therefore exists to prevent radiation from outside the desired target area from reaching the sensing element of a pyroelectric detection system despite the use of a relatively short focal-length lens in the system.